Some low-level comedi drivers (incorrectly) point `dev->read_subdev` or
`dev->write_subdev` to a subdevice that does not support asynchronous
commands. Comedi's poll(), read() and write() file operation handlers
assume these subdevices do support asynchronous commands. In
particular, they assume `s->async` is valid (where `s` points to the
read or write subdevice), which it won't be if it has been set
incorrectly. This can lead to a NULL pointer dereference.
Check `s->async` is non-NULL in `comedi_poll()`, `comedi_read()` and
`comedi_write()` to avoid the bug.
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
---
Note: this patch is for staging-next. Needs backporting for earlier
kernels.
---
drivers/staging/comedi/comedi_fops.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index c7377d0..4a28d75 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1844,7 +1844,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
}
s = comedi_read_subdevice(info);
- if (s) {
+ if (s && s->async) {
poll_wait(file, &s->async->wait_head, wait);
if (!s->busy || !comedi_is_subdevice_running(s) ||
comedi_buf_read_n_available(s->async) > 0)
@@ -1852,7 +1852,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
}
s = comedi_write_subdevice(info);
- if (s) {
+ if (s && s->async) {
unsigned int bps = bytes_per_sample(s->async->subdevice);
poll_wait(file, &s->async->wait_head, wait);
@@ -1887,7 +1887,7 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
}
s = comedi_write_subdevice(info);
- if (!s)
+ if (!s || !s->async)
return -EIO;
async = s->async;
@@ -1982,7 +1982,7 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
}
s = comedi_read_subdevice(info);
- if (!s)
+ if (!s || !s->async)
return -EIO;
async = s->async;
--
1.8.1.2
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